FR2680276A1 - METHOD OF CONTROLLING THE ENGRAVING PROFILE OF A LAYER OF AN INTEGRATED CIRCUIT - Google Patents

Abstract

The invention relates to a method for sloping etching a layer of an integrated circuit. The layer to be etched 1 is coated with a resist layer 2 forming a mask. The method consists in carrying out jointly a passivation P of the etching flank of the layer to be etched 1 and a non-isotropic erosion of the resist layer 2 forming a mask, which makes it possible to control the slope pe of the etching flank of the layer to be etched. 1. Application to the sloping etching of the interconnection layers of integrated circuits.

Description

i

  METHOD OF CONTROLLING THE ENGRAVING PROFILE

A LAYER OF AN INTEGRATED CIRCUIT

  The present invention relates to a method for controlling the etching profile of a layer of an integrated circuit. In addition to the dimensional control of the etching of the integrated circuit layers, the control of the etching profiles, that is to say the spatial law of etching in a direction orthogonal to the surface of the integrated circuit substrate, intervenes in a manner of more and more sensitive in the evolution of microelectronic etching techniques.15 Following the advent of dry etching, or plasma etching, the control of the profile of the vias formed in the isolation dielectric between levels In such a case, the solution consists in using an anisotropic etching, that is to say having only one component orthogonal to the surface of the substrate; in particular the dielectric layer such as Si O 2 The slope control is obtained by consumption or erosion of the resist mask (photoresist). As shown in Figure la) relating to a first embodiment of the technique However, this erosion can be isotropic, such erosion having however the disadvantage of too much sensitivity to the effects of charge, that is to say, surface to engrave, distance between patterns and size of the patterns. This erosion can also, as shown in FIG. 1b, be anisotropic. Such an erosion, however, requires profiling the reserve mask, that is to say, to adapt its profile prior to the etching process itself. Adaptation techniques used for this purpose usually include a heat treatment, such as creep, and prove unsuitable for the realization

  micron patterns and a fortiori submicron.

  With regard to the control of the etching profile of the interconnection materials, the latter, until now, has essentially been limited to that of the etching anisotropy, that is to say to the control of the vertical character , or orthogonal to the surface, of this profile As shown in Figure la, the anisotropic etching of a metal, such as aluminum, requires the passivation of the etching flank, that is to say the formation of a thin layer inhibiting the risk of lateral attack by the etching agent, which in this particular case is constituted by atomic chlorine from the C 12 molecule. Such passivation is most often obtained by formation and deposition of chloro compounds or volatile fluoro-carbon C Clx or C Fx from the consumption of the mask-forming reserve and / or the cracking of additional gases such as CC 14, CHC 13, CF 4, CHF 3, Si C 14 or NF 3. This mechanism inhibits etching by removing any etch component lateral re on the flanks of the metal. Thus, an anisotropic etching process for aluminum that can be used for the manufacture of integrated circuits, that is to say the consumption of which the spare mask remains compatible with the topographies of these circuits, can be implemented after a choice appropriate ionic plasma parameters, such as pressure

  This choice also depends on the design of the reactive ion etching reactor. Beyond the simple anisotropic etching, the control of the slope of the gaseous atmosphere, the radio frequency power, the gas flow, the gas mixture. profile of metallic materials

  This connection has the technological advantage of improving the planarizing power and the quality of the deposits of the upper layers, such as the intermetallic dielectric or encapsulation layers, whatever the dielectric deposition technique used, with the result that it is better maintained. and a better

  reliability of microchips in the medium or long term.

  However, the control of the etching profile of a metallic material, such as aluminum, by anisotropic erosion of the mask reserve, according to FIG. 1b, or by deposition of the polymers on the etching flanks by reinforcing the deposition component. Passivation of FIG. 1a, presents a solution that is difficult to industrialize. Indeed, such a result can only be obtained at the cost of too much consumption of the resist forming a mask or of an etching chemical environment which is too polymerizing and therefore generates particles and, consequently, defects in the definition of the metallic level. The subject of the present invention is the implementation of a method for controlling the etching profile of a layer, in particular a metal layer, of a circuit

  integrated, does not have the aforementioned drawbacks.

  Another object of the present invention is the implementation of a method for controlling the etching profile of a layer, in particular of a metal layer, of an integrated circuit allowing the use of reactions and little chemicals. or not polymerizing, which makes it possible to overcome the appearance of defects in the

  definition of the level of the layer, in particular the metal layer.

  Another object of the present invention is the implementation of a method for controlling the etching profile of a layer, in particular of a metal layer, of an integrated circuit enabling an etching process causing a low vertical consumption, in a direction orthogonal to the surface of the integrated circuit substrate, of the mask reserve, this consumption being, according to another object of the method which is the subject of the invention, rendered minimal, in order to adapt the method which is the subject of the invention to industrial operating conditions. The method of etching the profile of a layer of an integrated circuit, said layer to be etched, this layer being coated with a resist layer forming a mask, in accordance with the subject of the present invention, is remarkable in that that it consists in jointly carrying out a passivation of the etching side of said etching layer and non-isotropic erosion of said resist layer forming a mask, which makes it possible to control the slope

  the etching edge of the layer to be etched.

  The process which is the subject of the invention finds application in the industry of manufacturing integrated circuits in

the industrial scale.

  It will be better understood by reading the

  description and to the observation of the drawings below in

  which, in addition to FIGS. 1a, 1b, 1c relating to the prior art, FIG. 2a is illustrative of one embodiment of the method which is the subject of the present invention, FIG. 2b represents a diagram of the efficiency. e, as a percentage of a reactive ion etching erosion as a function of the angle of incidence i, expressed in degrees, of the ion flux from the plasma on an exposed face of the integrated circuit substrate, FIG. points a) to d), represents different steps of a first embodiment of the method which is the subject of the invention in which the etching of the mask reserve is performed for a minimal erosion of the flanks of the mask reserve, FIG. , at its different points a) to d), represents different steps of a second embodiment of the method which is the subject of the invention in which the flanks of the mask forming reservoir subjected to profiling are the seat of an erosio n more intense, which in fact makes it possible to ensure a transfer of the profiling of the flanks of the mask reserve at the level of the flanks of the layer

to engrave.

  The method of etching a layer of an integrated circuit according to the present invention will be firstly described in connection with FIG. In general, the method that is the subject of the present invention consists in performing the sloping etching of an integrated circuit layer by the conjunction of passivation of the etching flank and non-isotropic erosion of the resist layer. forming mask on the

  so-called layer to be etched of the aforementioned integrated circuit.

  In FIG. 2a, the layer to be etched bears the reference 1 and is coated with a reserve layer 2 forming a mask in two dimensions contained in a plane orthogonal to the plane of the sheet or plane of section of the

figure 2 a.

  According to a particularly advantageous characteristic of the method which is the subject of the invention, the latter consists in jointly carrying out a passivation, denoted P of the etching flank of the layer to be etched 1 and a non-isotropic erosion of the reserve layer 2 forming a mask. joint implementation of the two aforementioned operations to control the slope, noted pe, of

  etching edge of the layer to be engraved 1.

  In general, it will be understood that the control of the aforementioned slope pe of the etching flank of the layer 1 is obtained for a low consumption in the vertical direction of the resist layer 2 forming a mask and by the use, to realize the non-isotropic erosion of the aforementioned resist layer, for example a reactive ion etching process, in an etching medium having a very low polymerization activity, or

  the absence of chloro or fluorocarbon compounds.

  According to a first operating mode as represented in FIG. 2a, the method which is the subject of the present invention consists, in order to carry out the control of the slope of the etching side of the layer to be etched 1, to perform a profiling of the layer reserve 2 at the foot of the flank thereof Without limitation, the foot of the sidewall is defined as the lateral zone of the mask forming layer located in the vicinity of the layer to be etched 1, this lateral zone, as shown in section in Figure 2a, perpendicular to the surface of the layer to be etched 1 at the beginning of the implementation of the method object of the present invention, gradually becoming, during the process, inclined according to a slope pe of the fact non isotropic erosion of the resist layer 2 forming a mask

previously mentioned.

  Furthermore, in accordance with the aforementioned procedure, it then consists in simultaneously transferring the profiling of the resist layer 2 at the level of the layer to be etched 1 by anisotropic etching, symbolized by the accelerator electric field E of a flux The shaped resist layer 2 at the foot of the flank thereof is thus subjected to non-isotropic erosion due to the conjunction of the anisotropic etching caused by ion etching and the joint deposit. of a compound with low volatility on the foot of the flank of the aforementioned reserve layer. The conjunction of the two phenomena thus causes, on the one hand, the profiling of the resist layer 2 at the foot of the flank of the latter, and the transfer to the level of the layer to be etched 1 of the non-isotropic erosion, that is to say of the anisotropic etching by means of the reactive ion etching E and the passivation of the etching flank of the layer with g raver 1 The slope pe formed first at the level of the resist layer 2 is thus transferred to

  level of engraving edge of the layer to be engraved 1.

  In general, it will be considered that, in order to ensure the anisotropic nature of the reactive ion etching, this is carried out at low pressure, that is to say at a lower ambient gas pressure.

m Torr.

  In addition, the anisotropic nature of the reactive ion etching is ensured by a dilution of the reactive ionic etching atmosphere, this atmosphere possibly consisting of a chlorinated compound diluted in a neutral gas such as nitrogen or argon. It will be noted that the use of such a reactive ion etching atmosphere makes it possible to provide a purely physical etching component, that is to say caused by the only acceleration of the ions by the electric field E represented

in Figure 2 has for example.

  With regard to the deposition component forming the passivation P of the etching edge of the layer to be etched 1, and previously the profiling of the resist layer 2 at the foot of the latter's flank, such a deposition component can then be advantageously obtained by adding to the previously described etching atmosphere a low-volatility gas that does not directly produce a carbonaceous compound. Such a gas may, for example, consist of

by chlorosilane Si C 14.

  According to another operating mode also represented in FIG. 2a, the control of the slope pe of the etching edge of the layer to be etched 1 can advantageously be achieved by the simultaneous realization of a facetting of the resist layer 2 at the top of the flank of it thanks to

  previously mentioned anisotropic etching process.

  It will be noted that such a faceting operation makes it possible during the non-isotropic erosion step to concurrently generate a greater local consumption of the resist layer 2 at the edges of the faceting patterns and a formation of carbonaceous compounds. redepositing at the foot of the pattern and the layer to be engraved 2, which makes it possible to control the slope

  pe or engraving profile of the layer to be engraved 1.

  In general, it will be understood that the facetting of the resist layer 2 at the top of the flank of the latter is carried out at normal incidence to the reactive ionic plasma substrate symbolized by the arrow E. The above-mentioned plasma, as shown in FIG. 2 b, a maximum of sputtering rate for an incidence of between 40 and 600 relative to the normal, to the local surface of the substrate or to the mask reserve 2 In the aforementioned procedure, the facets generated by the operation of Facetting of the mask-forming resist layer 2 is obtained by preferential erosion, in the vicinity of the radius of curvature of the edges of the resist layer 2. The aforementioned facets as represented in FIG. 2a and noted f thus have an inclination with respect to the incidence direction of the plasma between 40 and 600 and thus correspond to the maximum of the spraying rate e as represented by FIG. gure 2 b, depending on the angle

incidence i.

  It will be noted that the phenomenon of faceting comes from the dependence of the sputtering rate e, due to the physical component of the reactive ion etching, vis-à-vis the angle of incidence of the ions The maximum spraying rate corresponds to an amplification of the consumption of the facets of the reserve layer forming

mask a factor of 2 to 10.

  In order to implement the faceting process as previously described, the physical component of the reactive ionic etching of the mask-forming resist layer must be important. Such a situation corresponds to a reduced chemical or reactive component, ie that is to say to the realization of the process of reactive ion etching in a regime of low consumption of mask-forming resist layer. Such an etching can be carried out at low pressure, that is to say at a pressure of reactive ion etching atmosphere. , that is to say less than 200 m Torr consisting of a reactive gas such as chlorine, C 12, diluted with nitrogen or argon, as previously described in connection with the process of transfer of the slope pe of the foot of the side of the layer of

reservation 2.

  It will be readily understood that the process of controlling the slope of the engraved profile can be carried out in accordance with one and / or the other of the previously described processes, i.e., via the one, process transferring the profiling of the resist layer at the level of the layer to be etched 1, and / or the other, that is to say the process of facetting the resist layer at the top of the flank thereof, previously described in

  description. It will be understood in particular that the process of etching by reactive ion etching must thus be

  carried out, in one and / or in the other case, using a gaseous mixture of the N 2 -C 12, Ar-C 12, N 2 -C 12 -SiC 14 type,

  Ar-C 12-Si C 14, N 2 -C 12-Si C 14 -BCA 13 or Ar-C 12 -Si C 14 -CB 13, which makes it possible to control the value of the slope of the profile etched by the one and / or the other of the previously mentioned processes.

  It should be noted that the radio-electric power or radiofrequency power applied to generate the reactive ion etching plasma depends, of course, on the etching reactor used, but must be sufficient to ensure the intrinsic anisotropy necessary for the aforementioned mechanisms. that in a practical way, the required power level remains quite standard. For the embodiment in a layer to be etched 1 constituted by an aluminum layer, the slope pe being 500 to 90 relative to the base of the integrated circuit substrate, it will be indicated that the etching etching rate

  aluminum should be in the range of 7000 to 13000 A / min, while the etch rate of the resist layer 2 forming a mask should be in the range of 2000 to 5000 A / min.

  It will be noted that the control of the slope pe is carried out directly by that of the composition of the etching atmosphere, that is to say by the proportions of nitrogen N 2 or argon Ar, or of C 12 and chlorosilane Si C 14.

  A more detailed description of one and / or

  the other process of controlling the slope pe of the etching edge of the layer to be etched 1 will be given in connection with

  Figure 3, respectively with Figure 4.

  In general, it will be considered that the method which is the subject of the present invention can be

  characterized by the fundamental element below.

  For an instantaneous angle of the foot of the resist layer 2 forming a mask, the instantaneous angle O of the etching edge of the layer to be etched 1 is such that the ratio of the tangents of the two angles is proportional to the ratio of the etching rate. apparent of the layer to be etched, denoted vcg, that is to say non-isotropic etching resulting from anisotropic etching in the vertical direction due to reactive ion etching and the competitive deposition of passivation, and the etching rate

  of the mask reserve, denoted vcr, minus a product term of the isotropic deposition rate of the passivation layer P, this speed being denoted D, by the tangent of the instantaneous angle of the foot of the resist layer. forming mask.

  The aforementioned angles verify the relation: tg e = vcg tga vcr-D tg "

  A more detailed description of the implementation of the control process of the etching profile of a layer

  An integrated circuit according to the present invention will be given in conjunction with FIG. 3 in the case where the mask-forming reserve layer does not comprise any initial pre-etching process, the flank of the mask-forming resist layer thus being substantially orthogonal. to the initial etching layer 1, respectively Figure 4, in the case where, on the contrary, the mask forming resist layer 2 is subjected to a pre-engraving process, the sidewall of the resist layer 2 forming a mask having an inclination or slope pe, this flank forming an angle α with respect to the surface of the layer to be etched 1. In accordance with FIG. 3, as represented at point a) thereof, the initial mask-forming reserve layer 2 has a flank orthogonal to the free surface of the layer to be etched 1, which is presumed to be horizontal. The process of etching proper by reactive ion etching symbolized by the arrow E makes it possible to go to point b) by constituting a non-isotropic erosion of the mask-forming resist layer 2, a profiling of this resist layer 2 at the foot of the flank thereof is effected by the creation of a slope flank pe, this flank of etching and the resist layer blank 2 being thus transferred at the level of the layer to be etched 1, because of the anisotropic etching E of the resist layer 2, as represented in the above-mentioned point b).

  during this process, the passivation P of the etching flank of the layer to be etched 1 is performed because of the presence of the erosion products of the layer 2 forming a mask.

  In point c) of Figure 3, the transfer process is maintained, which allows to maintain the slope

  eg the etching flank of the resist layer 2 forming a mask and, of course, the layer to be etched 1, because of the transfer of the profiling thus obtained.

  Finally, in point d) of FIG. 3, the layer to be etched 1 has been completely reduced, except as regards the part situated under the reserve layer 2 forming the final mask, the slope pe of the aforementioned resist layer 2 and the remaining part of the layer to be etched 1 is of course maintained It will of course be understood that the residue of the reserve layer 2 forming the final mask, as well as the passivation P present on the etching flanks of the layer to be etched 1 can then be be removed by any

  chemical treatment of conventional type adapted.

  Finally, it will be noted that during the process as represented in FIG. 3, and in particular in points b),

  c) and d) thereof, the faceting phenomenon characteristic of the implementation of the method that is the subject of the present invention has been demonstrated by the materialization of the facets f at the top of the intermediate mask resist layer. or final.

  In the case of FIG. 4, on the other hand, the original mask-forming reserve layer 2, prior to the actual etching process, has been subjected to a pre-etching step, which has the effect of generating slope etching flanks. inclined relative to the free surface of the layer 1 to be etched, assumed horizontal, the etching flanks of the initial mask forming resist layer 2 thus being inclined at an angle a20 with respect to the aforementioned free surface. the pre-engraving process may consist of a soft etching, which has the property of selectively attacking the initial mask forming layer 2, excluding an attack of the layer 1 to be etched to the contrary, the layer 2 reserve forming an initial mask may be deposited and treated so as to present etching flanks having the slope pe as represented in point a) of FIG. 4. The implementation of the procedure The object of the present invention as represented in point a) of FIG. 4 then makes it possible, by reactive ion etching, symbolized by the arrow E, to perform, on the one hand, the profiling of the etching flanks of the layer 2 of FIG. mask forming reserve, the joint passivation P of the etching edge of the layer 35 to be etched 1 and, finally, the transfer of the profiling of the aforementioned resist layer 2 at the level of the layer to be etched 1, according to the previously

  As mentioned in the description As shown in points b) and c) in particular in FIG. 4, the layer to be etched 1 then has an etching flank having an inclination at an angle e with respect to the free surface of the layer to be etched. engrave intermediate 1, the angle e verifying the

  aforementioned relation and corresponding to a slope inclination p'e obtained by transfer of the slope pe of the mask layer 2 reserve It will be noted of course that in the aforementioned relation, the engraving speed of the layer to be engraved vcg designates the engraving speed

  apparent or sharp in the vertical direction of the etching and the competitive deposit resulting from the erosion of the layer 2 forming the mask and constituting the passivation P of the etching flank of the layer to be etched 1.

  It will also be noted that in the aforementioned relation, D denotes the isotropic deposition rate of the products

  erosion of the mask forming layer 2, this isotropic deposition rate only being manifested by its horizontal component.

  At point D of FIG. 4, the final etched layer having the angle e previously

  mentioned, whereas the layer 2 of reserve forming mask has on the contrary at its flank of etching a corresponding angle α.

  It will be noted in all cases, as shown in points b), c), d), of Figure 4, that the faceting phenomenon is also obtained, this faceting phenomenon being represented by the notation f at the top of the layer 2

reserve forming mask.

  Examples of implementation of the method which is the subject of the present invention will now be given in the case

  etching of aluminum and, respectively, tungsten.35 Engraving of aluminum.

  Obtaining an angle profile e = 750 for: gas flow: 50 sccm Si C 14 40 sccm C 12 60 sccm Cl 2 pressure: 60 m Torr

  RF power: 300 W (2.4 Watt / cm 2).

  Obtaining an angle profile 9 = 85 for: gas flow: 40 sccm Si C 14 65 sccm Cl 2 70 sccm N 2 pressure: 110 m Torr

  RF power: 350 watts (2.9 W / cm 2).

  It will be recalled that in the previously mentioned values, sccm designates the abbreviation in Anglo-Saxon language for "standard cubic centimeter per minute", ie cm 3 / mn. On the other hand, it is recalled that, for

  As regards aluminum, the etching rate is between 7000 and 13000 A / min, while the etching rate of the mask forming resist layer is between 2000 and 5000 A / min.

Engraving of tungsten.

  It will be noted that with regard to the etching of a layer to be etched in tungsten, for example, in accordance with the method which is the subject of the present invention, such etching can be carried out in reactive ion etching (RIE) mode at a pressure of less than 200 m. Torr using a gas mixture of the N 2 SF 6, N 2 -NN 3, Ar-SF 6, Ar-NF 3, N 2 -SF 6-C 12, Ar-SF 6 -Cl 2 type, N 2-NF 3 -Cl 2, Ar-NF 3-C 12. The use of the aforementioned gas mixtures, under the aforementioned pressure conditions, makes it possible to control the slope of the profile etched in accordance with one of

  and / or the other of the slope control processes previously described in the description. Of course, it will be appreciated that the applied RF radio-frequency power is dependent on the etching reactor, but should be sufficient to provide the intrinsic anisotropy necessary for the proposed mechanism.

  With particular reference to tungsten, the operating conditions were as follows: tungsten etching rate: 2,000 to 10,000 A / min, etching rate of the resist layer forming a mask: 1,000 to 10,000 A / min, angle at the foot of the layer

  of photoresist by pre-engraving: 60 to 900.

  An example of implementation made it possible to obtain the following results for tungsten: obtaining an etching profile at 750 for: gas flow rate: 50 sccm SF 6 20 sccm N 2, pressure: 150 m Torr,

power: RF 250 Watt (2 W / cm 2).

  Thus, a method of sloping etching of a layer of a particularly efficient integrated circuit has been described, since the method which is the subject of the present invention makes it possible to effect the sloping of layers of integrated circuit material, such as layers aluminum or tungsten metal, or even non-metallic layers such as polysilicon. In general, it will be considered that the layers that can be etched in accordance with the implementation of the method of the present invention are, on the one hand, aluminum-type layers, this material can also be doped with materials such as silicon, titanium, copper, silicon and copper and silicon and titanium alloys, these layers may further comprise a barrier or bonding sub-layer such as layers of titanium, titanium nitride, Ti N, of the alloy, Ti W, and, on the other hand, the interconnection materials, of the tungsten type, which may also comprise a barrier sub-layer or

hooking.

Claims (7)

  1) A method of etching a layer of an integrated circuit, said layer to be etched (1), this layer being coated with a resist layer (2) forming a mask, characterized in that said method consists in carrying out jointly: a passivation (P) of the etching side of said etching layer (1), a non-isotropic erosion of said resist layer forming (2) mask, which makes it possible to control the slope   (pe) the etching edge of said layer to be etched.   2) Process according to claim 1, characterized in that, in order to perform the control of the slope of the etching side of said layer to be etched (1), said method15 consists simultaneously: to perform a profiling of said layer of reserve (2) at the foot of the sidewall thereof, to perform the transfer of the profiling of said resist layer (2) at said etching layer (1) by anisotropic etching (E) of said resist layer (2) said profiled resist layer subjected to anisotropic etching (E) thus being subjected to said non-isotropic erosion.   3) Method according to one of claims 1 or 2,   characterized in that, for controlling the slope (pe) of the etching side of said etching layer (1), said method comprises simultaneously faceting said resist layer at the top of the flank of said by anisotropic etching (E), which allows the course of said non-isotropic erosion step to concurrently generate a greater local consumption of the   a resist layer (2) at the edges of the patterns of said faceting and a formation of carbon compounds redeposing at the foot of said pattern and the layer to be etched (2), thereby making it possible to control the slope (pe) or engraving profile of the layer to be etched.   4) Method according to one of claims 1 to 3 characterized in that the anisotropic etching is performed   by reactive ion etching (E), at low pressure. 5) Method according to claim 4, characterized in that said reactive ion etching (E) is performed in an atmosphere consisting of a chlorinated compound and / or fluorinated   diluted in a neutral gas. 6) Method according to one of claims 2 to 5 characterized in that for an instantaneous angle of the foot of   the mask-forming reserve layer (2), the instantaneous angle e of the etching flanks of the layer to be etched is such that the ratio of the tangents of the two angles is proportional to the ratio of the etching rate vcg apparent of the layer to be etched (1) and the etching rate of the vcr mask reserve decreased by one term, produces the isotropic deposition rate of the passivation layer P by the tangent of the instantaneous angle of the foot of the resist layer. forming mask, tge = vcg tga VCR-D tga   7) Method according to one of claims 4 to 6, characterized in that the facetting of said layer of   reserve (2) at the top of the flank thereof is effected without normal incidence to the reactive ionic plasma substrate (E), said plasma having a maximum sputtering rate for an incidence of between 40 and 600 relative to the normal to the local surface of the substrate or the mask-forming reservoir, the facets generated by the facetting operation of the mask-forming resist layer (2) being obtained by preferential erosion in the vicinity of the radius of curvature of the edges of the protective layer;   reserve (2) and thus having an inclination, relative to the direction of incidence of the plasma, between 400 and 600, corresponding to the maximum of the spraying rate.